Method of treating sulfur containing mineral oils to reduce their sulfur content

ABSTRACT

A METHOD OF TREATING SULFUR-CONTAINING MINERAL OILS TO REDUCE THEIR SULFUR IS DISCLOSED IN WHICH THE OIL IS CONTACTED WITH SUPERHEATED WATER, FOR EXAMPLE, BY COUNTER-CURRENT EXTRACTION TECHNIQUE.

Sept. 25, 1973 EL MUNEKATA ET AL 3,761,398

METHOD ,OF TREATING SULFUR-CONTAINING MINERAL OILS TO REDUCE THEIRSULFUR CONTENT Filed Jan. 26, 1971 I2 3 LT. 41 1 fr up United StatesPatent G 3,761,398 METHOD OF TREATING SULFUR-CONTAINING MINERAL OILS TOREDUCE THEIR SULFUR CONTENT Eiji Munekata, Tokyo, and Eisuke Munekata,Toyonaka, Japan; said Eisuke Munekata assignor to said Eiji MunekataFiled Jan. 26, 1971, Ser. No. 109,892 Claims priority, applicationJapan, Feb. 16, 1970, 45/ 12,664; May 28, 1970, 45/45,179 Int. Cl. Cg17/08, 29/08 US. Cl. 208-408 ABSTRACT OF THE DISCLOSURE A method oftreating sulfur-containing mineral oils to reduce their sulfur contentis disclosed in which the oil is contacted with superheated water, forexample, by counter-current extraction technique.

BACKGROUND TO THE INVENTION Consumption of petroleum products as fuelhas been increasing steadily each year, accompanied by such publicnuisance as air pollution as a consequence. To fight against this publicnuisance the stress has been placed more and more on the removal ofsulfur contained in such fuel oils, including petrol, kerosene and lightoils as well as in crude oil and heavy oils.

There are a large number of different kinds of sulfur compounds presentin mineral oils, ranging from simple compounds such as hydrogen sulfideto complex mercaptanes, sulfides, di-sulfides, thiophenes, etc. Priorprocesses for reducing the sulfur content of mineral oils have tended toinclude different processing steps for removing the different kinds ofsulfur compounds. Such prior processes have, therefore, been complicatedand expensive and a need exists for a simple and more effective process.

It is therefore the primary object of the present invention to provide anovel method for reducing the sulfur content of mineral oil which isless complex and expensive than traditional processes.

An additional object of the present invention is to provide anextraction apparatus suitable for carrying out the novel method.

Further objects and advantages of the invention will become apparentfrom the following description.

SUMMARY OF THE INVENTION It has been discovered by the inventors that alarge number of different kinds of sulfur compounds present in mineraloils can be removed by extraction with superheated water, i.e. watermaintained at superatmospheric pressure and having a temperature higherthan 100 C.

Although the sulfur compounds contained in mineral oils can be dissolvedin superheated water, the amount of the dissolved sulfur compounds isgoverned by the law of distribution between mineral oils and superheatedwater. By the law of distribution a higher concentration of sulfurcompounds will dissolve into the oil phase than in the water phase. Theabsolute amount of sulfur compounds dissolved into water, however,increases if the amount of water is increased in proportion to theamount of oil. The total amount of dissolved sulfur compounds is furtherincreased if the oil and water are brought in contact counter-currently.

Extraction towers may be used in an industrial scale. However, it may bemore effective to use extraction vessels which are connected in series,and operate the method by a counter-current extraction of the oil with.superheated water. Incidentally, superheated water and hot mineral oildo not easily mix with each other. It is there- 5 Claims 3,761,398Patented Sept. 25, 1973 fore essential to adjust the fluidity of bothliquids, so that the superheated water and hot mineral oil intimatelycontact each other. When the extraction is carried out with superheatedwater in an extraction tower, it is essential that there is a differencein specific gravity (density) between the two liquids, so that there isadequate countercurrent flow. For this purpose the inventors recommendtwo methods, i.e. either to adjust the specific gravity of thesuperheated water by addition of water soluble substances and/or byapplication of colloidal solution or to adjust the specific gravity ofthe sulfur containing mineral oil by application of distillates and/orby addition of heavier or lighter oil, as required. At any rate, theadequate difference in the specific gravity is vitally important for theextraction process to be performed satisfactorily in the extractiontower. In this extraction there is a close relationship between thespecific gravity and the fluidity. When the difference in fluiditybetween the superheated water and the sulfur containing oil is small,the difference in specific gravity can be small. And when saiddifference in large, it is necessary to increase the difference inspecific gravity. Should the difference in the specific gravity be toolarge, both superheated water and sulfur containing oils merely runagainst each other without coming into intimate contact with each other,with consequent insufficient extraction. If, on the other hand, thedifference in the specific gravity is too small, then there will be nocounter-current contact of sulfur-containing mineral oils withsuperheated water and therefore effective superheated water extractionbecomes impossible.

It is difficult for superheated water to come into intimate contact withsulfur-containing mineral oil, therefore migration of sulfur compoundsfrom the mineral oil into the superheated water does not take placeunless the superheated water and sulfur-containing mineral oil have asubstantially similar fluidity. It is a common sense in liquid-liquidextraction to resort to agitation and other means similar thereto inOrder to obtain a good mutual dispersion. To control the fluidity, itmight also be neces sary to adjust the relative proportions ofdistillates in the sulfur-containing oils. For instance,sulfur-containing heavy oil and desulfurized light oil can be mixed inorder to prepare a sulfur-containing mineral oil having an ade quatefluidity for the superheated water extraction. The oil mixture aftertreatment can be separated into heavy oil and light oil by distillationin order to achieve the object of heavy oil desulfurization.

To explain the extraction condition, the inventors have decided toadjust the relative specific gravities of the mineral oil andsuperheated water for achieving satisfactory counter-current flow, andthe inventors find no contradiction as to the explanation oncounter-current extraction from the viewpoint of relative fluidity,because what the specific gravity and the fluidity mean here arecompatible. The inventors are of an opinion that the adjustrnent of thedifference of the specific gravity is a basically important conditionfor the execution of superheated water extraction based on thecounter-current contact technique. It is also a fact that liquid with asmall specific gravity has a high fluidity, while a liquid with a largespecific gravity has a low fluidity as far as petroleum mineral oils areconcerned, within the range of this invention. Therefore, the inventorslay greater weight on the specific gravity of the mineral oils and thesuperheated water in determining the working conditions of the methodand less weight on fiuidities of the liquids.

In order to adjust the difference between the relative specificgravities of sulfur-containing oils and of the superheated water oraqueous solution (neutral, acidic or basic solution), it is convenientto adjust firstly the concentration of additives to the superheatedwater. For this purpose it is recommended to apply inorganic or organicsolutions, and/or suspensions or emulsions, namely colloidal solution.For instance, the use of such solutions as salt solution, or a solutionof iron sulphate in which iron hydroxide is suspended can berecommended. Howver, it is better to employ water itself, if possible,because a Water solution generally has a lower dissolving power thanwater itself. If the required difference of the specific gravity isfound to be difficult to obtain, when superheated water is used, it isrecommended to facilitate the adjustment of the difference of thespecific gravity by appropriate adjustment of the specific gravity ofthe sulfur containing oil. The inventors recommend use of superheatedwater itself for treatment of sulfur-containing lighter oils and use ofsuperheated water solutions for the treatment of sulfur-containingheavier oils. The changes in the specific gravities of mineral oils andwater with temperature are not always parallel. For example, thespecific gravity of superheated water falls more rapidly with risingtemperature than that of mineral oils; above a certain temperature,water has a specific gravity which is smaller than that of mineral oils.Thus, at the higher temperatures it becomes necessary to use watersolutions.

The temperature used in the superheated water extraction methodaccording to this invention is more than 100 C. As the preferable rangeof this temperature is 100 to 350 C., both sulfur-containing mineral oiland superheated water must be kept at this temperature. The extractiontower must be maintained at a pressure much higher than the totalpressure of both partial pressure of vapor of water and partial pressureof the vapor of mineral oil. By so doing, the boiling of either water oroil inside the extraction tower can be supressed, which otherwise woulddisturb the regular counter-current flow of the liquids. Thequantitative relations between the sulfur-containing mineral oils andsuperheated water or superheated water solution, the relations betweendifferences of specific gravities as well as the temperature conditionsfor the extraction, must be determined for each experimentindependently.

As it is apparent from the above stated description, the desulfurizationof sulfur-containing mineral oils utilizing the dissolving power ofsuperheated water in respect of sulfur compounds is proved by thedescription of autoclave experiment in Ex. 1. However, an extractionequipment is required to carry out the desulfurization ofsulfur-containing oils with superheated water on an industrial scale.This equipment must have such function as to enable sufficient mutualdispersion of mineral oil and of superheated water. The equipment mustbe made of corrosion proof material in order not to be affected bysulfur-containing mineral oil and superheated water, particularlysuperheated water solution which contains neutral, acidic or basicsubstances. In order to have a thorough mutual dispersion, fillingmaterials must be charged into the extraction tower, or agitators mustbe installed in the extraction tower or in a multiple of extractionvessels, connected in series. The regular and constant counter-currentflow of the superheated water and sulfur-containing oil in theextraction equipment will be considerably prevented if boiling of eithermineral oil or superheated water takes place. It must also be soarranged that a pressure much higher than the total pressure ofsuperheated water vapor and mineral oil vapor, must be introduced intothe extraction equipment. The inventor also recommends recovery of thepressure of the superheated water and mineral oil being discharged fromthe extraction equipment to save the power necessary for theintroduction of mineral oil and superheated water under such anexcessive pressure.

DETAILED DESCRIPTION OF THE DRAWING A preferred embodiment of theinvention has been chosen for purposes of illustration and descriptionand is shown in the accompanying drawing. The drawing illustrates a casewhereby the extraction is made not by a multiple of extraction vesselsbut by an extraction tower. Reference numeral 1 indicates a superheatedvertical extraction tower, resistant to a high pressure, having an inlet2 for the superheated water at its upper part, and an inlet 3 for hotmineral oil at its lower part. Tower 1 also includes an outlet 4 of thedesulfurized mineral oil at its top, and an outlet 5 for thesulfur-containing superheated Water at its bottom. The superheated waterextraction tower 1 is either filled with inert filler materials or hasan agitating mechanism inside in order to sufficiently bring bothsuperheated water and the mineral oil, which is dispersed in thesuperheated water, in counter-current contact. Reference numeral 10indicates a water tank and reference numeral 11 a mineral oil tankcontaining the mineral oil which is to be treated. Tanks 10 and 11 areconnected via pressure pumps 8 and 9 to the tower 1. These pumps areconnected further to the interior of the superheated water extractiontower 1 via a heat exchanger 7 and heater 6. An outlet 4 for thedesulfurized oil and an outlet 5 of the sulfur-containcontainingsuperheated water are connected by pipes via heat exchanger 7 to thepressure recovery mechanism attached to pumps 9 and 8. These two outlets4 and 5 are so arranged that they are connected to desulfurized oilreceiving tank 13 and sulfur-containing water receiving tank 12. Thetemperature of the sulfur-containing water drops in the heat exchanger.Said sulfur-containing water is then led into the receiving tank 12. Asthe sulfur compounds cannot exist in dissolved state in water or watersolution according to the temperature depression, the sulfur compoundsare separated from aqueous phase, and exist as another liquid phase,even if said sulfur compounds be in a liquid state.

It can be seen that water or water solution and sulfurcontaining mineraloil stored in the water tank 10 and the oil tank 11 respectively will befed into the heat exchanger 7 by the pumps 8 and 9, where they are preheated as the result of the heat exchange with the desulfurized mineraloil and sulfur-containing superheated water or sulfur-containing watersolution which were already treated in the extraction tower 1. They willthen be forwarded to the heater 6 where they are heated to theappropriate temperature for the treatment and fed into superheated waterextraction tower 1 through superheated water inlet 2 and hot mineral oilinlet 3 at a pressure determined by the pressure pumps 8 and 9.Superheated water or superheated water solution as well as hot mineraloil fed into the extraction tower 1 are brought into counter-currentcontact, extracted, treated and recovered through the outlets 4 and 5,wherefrom they are conveyed via heat exchanger 7 to the desulfurized oilreceiving tank 13 and the sulfur-containing water receiving tank 12 tobe stored. Thus, the desulfurized mineral oil is obtained.

It will be appreciated that the operation pressure of the pumps 8 and 9must be maintained at a level which is high enough to suppress boilingof either the water or the oil. The pressure required is the grand totalof the partial pressure of superheated water and the partial pressure ofhot mineral oil found in the extraction column, plus the pressure of thepump required for transporting the fluid in the equipment, plus thepressure for pressurizing the extraction tower as a safety measure inorder to prevent bumping. As such high pressure is employed in theextraction, one of the features of this invention is to recover theenergy possessed by the pressure of the fluids discharged from thetower. For this reason a recovering apparatus is attached to thepressure pumps 8 and 9 in order to recover the pressure of desulfurizedmineral oil and sulfur-containing superheated water or sulfur-containingsuperheated water solution coming from the outlets 4 and 5 and flowingout of heat exchanger 7. The recovered heat energy pre-heats the rawmaterials which will become superheated water or superheated watersolution and hot mineral oil to be fed into the extraction tower andthereby saves the heat. The pressure energy recovering apparatus isinstalled in the pressure pumps 8 and 9, and takes the form of, forexample, a turbine operated by the pressure of the fluids dischargedfrom the tower. The turbine may be geared to the motors of the pumps 8and 9 for the purpose of saving the energy required by the motors of thepressure pumps. In order to economize electric power for the pressurepumps, it is possible to utilize said recovered pressure for electricpower generation by driving a power generator separately installed.

The following examples are given to illustrate the operation of themethod of the present invention.

EXAMPLE 1 A heavy oil with sulfur content 3.4% and specific gravity 0.97was charged into an autoclave together with water in an amount equal totwice that of said heavy oil. After agitation for about 20 minutes at atemperature of 300 C., the contents were allowed to settle, so that thewater phase separated from the oil phase and the two phases wereseparated. At this time, the sulfur content of the substance in the oilphase was 2.0%, and the sulfur content in the heavy oil dropped down toabout 40%.

Based on the confirmed finding of this autoclave experiment furtherextraction revealed that more than 50% of the sulfur contained in theheavy oil can be removed by continuous counter-current treatment. Inthis connection reference may be made to the experience of the inventorsin the counter-current superheated water extraction of phenols fromphenols-containing mineral oils (see Separation, Dr. Eiji Munekata,published by Maruzen, 1951, and Researches in the Chemistry andIndustrialization, Dr. Eiji Munekata, published by Nikkan KogyoShimbunsha, 1964).

EXAMPLE 2 Vacuum distilled gas oil (650-1000 F.) having a sulfur contentof 2.5% and a specific gravity 0.92 was extracted by superheated waterat about 230 C. in a counter-current contact extraction column in alaboratory. The sulfur content of the light oil after the treatment was1.5%. According to this result it is apparent that desulfurized gas oilwith sulfur content less than 0.5% could be obtained in an extractiontower operated counter-currently.

EXAMPLE 3 A heavy oil having a sulfur content of 4.4% and specificgravity 0.99 was blended with light oil in equal amounts to prepare asulfur-containing mineral oil of total sulfur content 2.5% and specificgravity 0.93. When examined, this blended oil was found to be far moresuitable than the original heavy oil for counter-current continuousextraction. This sulfur containing mineral oil was treated in theapparatus described in the drawing with salt water solution at 300 C. Aheavy oil was obtained by distilling the treated blended oil whichexhibited a reduction in sulfur content.

What is claimed is: 1. A method of treating a sulfur-containing mineraloil to reduce its sulfur content comprising extracting sulfur-containingsubstances from said mineral oil by intimately contacting said mineraloil with super-heated aqueous liquor having a temperature above C.,wherein the specific gravity of at least one of said mineral oil andsaid super-heated aqueous liquor is adjusted prior to treating said oil,by adding Water soluble substances and/ or colloidal substances so thatthe ditference between their specific gravities at the temperature ofthe treatment is sufficient to enable a counter-current flow.

2. The method of claim 1, wherein said aqueous liquor is at atemperature between 100 C. and 350 C. and said oil is contacted withsaid super-heated liquor in a treatment vessel.

3. The method of claim 1, wherein said super-heated aqueous liquor issuper-heated water.

4. The method of claim 1, wherein the specific gravity of the oil isadjusted by selecting suitable fractional distillates.

5. The method of claim 1, wherein the specific gravity of the mineraloil is adjusted by adding distillates to said mineral oil which is to betreated.

References Cited UNITED STATES PATENTS 2,78%59 3 1957 McDonald 23-310415,876 11/1889 Minshall 208-208 1,838,029 12/1931 Isles 208-2082,402,799 6/ 1946 Arnold et al 208-208 3,670,896 6/1972 Hale, Jr., etal. 210-242 DELBERT E. GANTZ, Primary Examiner J. M. NELSON, AssistantExaminer U.S. Cl. X.R. 208-289

